Johnson wanted to expand the war. Johnson wasn't tricked by McNamara into expanding the war. Johnson chose escalation and ordered McNamara to do it. McNamara obliged.

Look at the section beginning around 1:02:05 of this movie, where Johnson tells McNamara what kind of policy he wants.

They give us guns and drugs
Then wonder why in the fuck we thugs
They wanna count the slugs
Then come around here and fuck with us
They give us guns and drugs
Then wonder why in the fuck we thugs
They wanna count the slugs
Then come around here and fuck with us
I'm from the land of the gang bang
Since I was little, ain't a god damn thang changed
It's the same ol same
Bush run shit like Sadaam Hussien
I cock and aim, clinically insane
To deal with this bullshit day to day
If I sell some yay or smoke some hay
You bitches wanna throw me up in Pelican's Bay
Call me an animal up in the system
But who's the animal that built this prison
Who's the animal that invented lower living
The projects, thank god for Russell Simmons
Thank god for Sugarhill
I'm putting a different kind of steel up to my grill
Y'all know what it is, scared for your own kids
How these ghetto niggas taken over showbiz
They give us guns and drugs
Then wonder why in the fuck we thugs
They wanna count the slugs
Then come around here and fuck with us (Uh huh)
They give us guns and drugs
Then wonder why in the fuck we thugs
They wanna count the slugs
Then come around here and fuck with us
It's Boyz in the Hood, it's toys in the hood
Y'all wanna know why there's noise in the hood
Cause there's drugs in the hood, thugs in the hood
Nigga killed a Crip and a Blood in the hood (For real)
Cause when niggas get tribal
It's all about survival, nobody liable
I got caught by Five-0
Grandmama came to court with her bible
But when the judge hit the gavel
Now I'm too far from my family to travel
I just came unraveled
Socked the D.A. before I got gaffled
Owned by C.A, State Property
Just like the year fifteen fifty three
Looking for me, a one-way ticket out
Don't understand, what's so hard to figure out?
They give us guns and drugs
Then wonder why in the fuck we thugs
They wanna count the slugs
Then come around here and fuck with us (Uh huh)
They give us guns and drugs
Then wonder why in the fuck we thugs
They wanna count the slugs
Then come around here and fuck with us
I can't take the pressure
Pulled the fo-fo up out the dresser
Grabbed the weight up out the closet
Po-po coming but I'm scared to toss it
Y'all know what happened last time I lost it
Can't tell you niggas what the fuckin boss did
D game got a nigga exhausted
Gotta go for the plea bargain they offered
Twenty years for what?
Breaking these laws that's so corrupt
Taking these halls and fillin 'em up
Some powder cake shit that's about to erupt
Ay y'all, I'm about to be stuck
Until the year two thousand, what the fuck?
In the hood, don't press your luck
Cause these motherfuckers will set you up, word up
They give us guns and drugs
Then wonder why in the fuck we thugs
They wanna count the slugs
Then come around here and fuck with us (Uh huh)
They give us guns and drugs
Then wonder why in the fuck we thugs
They wanna count the slugs
Then come around here and fuck with us
Every hood's the same
Every hood's the same
Every hood's the same
Every hood's the same
Every hood's the same, stop trippin on it

Bob is an unreliable narrator, as Errol Morris knows all too well. Perfectly candid about things that make him look good (the Cuban missile crisis), and somewhat remorseful about his role in the firebombing of Japanese cities, he nonetheless remains evasive about Vietnam. He alone knew that Kennedy wanted out, and that the CIA was not a trustworthy source of intelligence... but Bob disagreed, and used his position to manipulate Johnson into a no-win situation. Did McNamara help prevent WW3 with the Soviets in 1962 and after? Was he responsible for millions of dead and wounded? Errol lets you be the judge. This is a must-see film for every American.